The use of heated or cooled water for heating or cooling a building and, when required, to serve sprinkler heads for combatting a fire is not new, having been suggested, for example, in U.S. Pat. Nos. 3,918,525, granted Nov. 11, 1975 and 4,033,740, granted July 5, 1977, and in reference cited thereagainst. The earlier of the indicated patents suggests sprinklers connected to the inlet lines for air conditioning apparatus so that flow, when a sprinkler is in operation, is divided between the apparatus and the sprinkler; a flow detecting switch is also disclosed in the line to the sprinkler to enable detection of flow to a sprinkler, and location of the sprinkler involved, if desired.